Method of treating-filaments.



I, WOOD. METHOD OF TRBATING= FILAMENTS. APPLICATION FILED FEBLQ, 1907.

meme

a May 21,1912.

Witne sses thereby heating it up ducing t e time'required-g'ior treating with v higher temperature .dliid ififi @ATEF? @EFFEQR HOW-Aw I. WOOD, CF SCHENEGTADY, ItIE H YORK, ASSIGNOR 'IQ GENERAL ELECTBIG COMPANY, A CORPORATION OF I-IEW YORK.

METHOD UT Til-EATING FILAMENIS.

Modded.

Specification of Letters Eatcnt.

raeemeana ei,

application filed February 9, 1997. Serial No. 35%,559.

To all wham'it may concern: a

' Be it known that I, HOWARD I. Woes, a itiz en [of the United States, residing at Schenectady, in the county of Schenectady and State of New York, have invented oer.- t-ain-new and useful Improvements in Methods of Treating Filaments, of which the following is a specification. I

My present invention relates to the manufactors of incandescent lamp filaments particularly filaments of high fusing metal such as tungsten, molybdenum, titanium, by the use of a vaporizable binder, and its object is to render the process of manufacture more expeditious and cheaper, to decrease the breakage of the filaments in carrying outthe process, and to improve it in other particulars.

The invention comprises an improvement in the process of filament manufacture invented by William D. Coolidge, and contemplates a novel apparatus for carrying out certain steps of the treatment.

The Coolidge process, above referred to, consists in mixing powdered metal such as tungsten, with a ductile binding means,such as warm cadmium amalgam, heating the mixture to a plastic condition, and then extruding the mixture so formed to produce ductile wires. These wires are then treated to drive out the mercury and cadmium. A coherent body of the refractory metal is left behind. A mixture suitable for this treatment consists of equal parts mercury and cadmium, to which is added 39% by weight of powderedtungsten. A simple method of driving out the mercury and cadmium consists in. passing an electric current through the ductile wire while in a. vacuum, and to the temperature at which the low tusing me ';als distil out. The filaments, may then be heated to a much to sinter the tungsten Such a treatment, however, must be given to the filaments individually and requires several seconds time for each filament.

According to my present invention, the filaments are heated a furnace to drive out substantially'all the mercury, and possibly a small uantity ofthe cadmium, the fehy reinto astrong wire.

current according to subsequent s epssoi th Coolidge process. According to my invention the filaments are treated in quantities or a hundred or more, simultaneously. The

distillation of the volatile metal may, by my method, be carried on slowly and the slow distillation obviates the danger of flaws or of checks in the finished filaments. I dQdlOt contemplatecomplete removal of the cadmium by my improved treatment, as such a proceeding would be liable to leave a residue too fragile for commercial purposes. By taking out only the mercury, the cadmium remains to give the filament strength and permit mounting in treating bottles, where current may be passed-through to distil the cadmium and sinter the particles of tungsten together.

Not only does invention decrease the time necessary for the production of a oompletedfilament, but it also decreases the percentage of breakage during treatment. The

wires of cadmium amalgam mixed with tungsten are initially quite strong and duc tile, but when heated up to the temperature atwhich mercury distils, they become soft and somewhat delicate, and in fact, must, at this stage, be carefully handled. As soon, however, as the mercury is all out, the filaments become strong again and may be handled Without dithculty. When the filaments are baked in the furnace, according to my invention, they pass through this delicate stage while resting in bundles on the carbon boats,and they are therefore not subjected to any stresses tending to break or deform them. The bundles of filaments come out of the furnace wit-hall the filaments intact and the treatment is in a sense independent oi the experience of the operator. I

An apparatus suitable for carrying out my process is shown in the accompanying drawing, in which- Figure 1 is any elevation of the vacuum furnace, Fig. 2 is a sectional view thereof; Fig. 3 is a diagram of the electrical connection of the electricheater, and Fig. 4. is a closed byasuitable cap 3. lVithin this glass envelop placed an electric heater el carrying carbon boats 5 on which the filaments are arranged in groups. Suitable connections (3 are provided for introducing current through the walls of. a glass vessel to the conductors of the heater.

The electric heater consists of a plurality of iron coils 7 connected in parallel and inclosed between sheets of mica 8. An aluminum plate 9 is a rrangcd below the resistance coils and serves to hold them in place and also to thermally insulate the coils from the lower wall to the glass envelop. The carbon or graphite boats 5 are provided with longitudinal grooves 10 in which the looped filaments 11 are arranged. A heavy copper plate 12 is interposed between the boats and the hot eoilsand serves to equalize the heaton the boats and thereby insure uniform heating of the tilamentsfl Tn treating filaments according to myinrention, the untreated wire of cadmium anialgain'impregnated with tungsten is cut into suitable lengths for filaments, bent into loops and arranged in the carbon boats as shown in Fig. 4. Several of these boats are then introduced into the furnace, as shown in Fig. l, and the cap 3 is placed on the end of the furnace and the furnace chamber is evacuated. Current is then supplied to the resistance coil 7 and the temperature within the furnace is slowly raised until the distillation of mercury is effected. A temperature of 215 C. gives good results, but a more rapid distillation may be etfected by running the furnace at a somewhat higher temperature. At presentl believe that some cadmium comes off with the mercury even at temperatures below the normal vaporizing point of cadmium, but sufiicient cadmium remains in the filaments to render them strong and suitable for ready manipulation according to subsequent steps of the Coolidge process. \Vhen a temperature of about 215 is used the heat treatment may be continued fora period of nzinutes. The filaments are then allowed to cool, and after removal from the furnace are separated and treated individually with current as in the original Coolidge process. This current-- drives out the remaining vaporizable components and sintnrs together the tungsten particles into a strong coherent filament.

The use of my invention in conjunction with other steps of the Coolidge treatment so shortens the work and decreases the breakage that the output of filaments, for a given nuu'ibcr of operators, may be increased fully four fold. 7

ll hat I claim as new and desire to secure by Letters Patent of the United States, is,

i. As a step in the production of metal I filaments, the process which consists in i'ltllf- 1 filaments, the process which consists in bak-.

mg a composite wire rendered coherent'by the presence of vaporizable metal to drive an easily vaporizable portion of such metal therefrom, and then heating said wire with current: to drive an additional. portion of vaporizable metal thercfrom'and sinter the residue.

4. As a step in the production of lamp filaments from a mixture of refractory metal and metallic material comprising a plurality of low melting metals, the process which consists in baking the mixture to drive out a less refractory portion of said material and thus produce filament shaped conductors which may subsequently be material and sten.

5. The process which consists in baking wires comprising a refractory powder incorporated in an amalgam containing vaporizablematerial to drive mercury thereyield filaments of pure tungfrom, and subsequently passing current through said wires to drive out any easily vaporizable material and sinter the residue into a. coherent refractory conductor.

6. The process. of treating a composite conductor composed of refractory metal powder held by a. less refractory alloy, which consists in heatingthe wire by external means to drive-out part of the material of said alloy, thcn heating said. wire;

with current passed therethrough to drive out theremainderof said alloy, continuing the heating to sinter the final residue into a coherent refractory conductor suitable for lamp filaments.

7. Asa step in the production of refractbryconductorg the process Which consists in treating 'byrradiant heat a filauu-ntarv body, composedof highly refractory met:

held together'by a binder having com ncnts of different degrees. of rcfractormess, so as to expel a COIHIJOIHTlt of the blnderofi low.

treated to drive out the remainder of said refractoriness, and, then passingan electric 1 current through said body to heat it. to

higher temperature, so as to expel the rest; of the binder andlcave only the pure metal and to sinter the highly. refractoryresidue.

8. As a step in the production of lilaments, the process which consists in baking a filamentary body containing highly rcf reetory material and metallic material of In witness whereof, I have hereunto set relatively low refractoriness by the presenge my hand this 7 th day of February, 19( 7.

j ldf which it is rendered coherent to, expel a .HOl/VARD I. WOOD. l pqrtion of the latter and produce a c0nducvvVVitnesses: t 5' tor consisting of highly refractory material BENJAMlN B. HULL,

angle-more refractory portion of said latter. Y HELEN ORFORD. 

